The present invention relates to a flame-retardant composition superior in abrasion resistance and further relates to a coating material or insulating material using the said flame-retardant composition. More particularly, the present invention is concerned with an abrasion-resistant flame-retardant composition which does not evolve a poisonous gas such as halogen gas during combustion and which has an anti-dripping property based on the formation of char, retains flexibility, mechanical characteristics and resistance to chemicals and is superior in heat resistance. The present invention is further concerned with a coating material or insulating material using the said flame-retardant composition for coating or insulating electric wires and cables, for coating electric wire or cable protecting pipes or joint covers, or for coating or insulating electric components and devices such as cabinet, box and sheet.
Polyolefin resins, because of their superior physical and chemical properties, are general-purpose resins which are in the greatest demand and which are applied to many domestic and industrial uses after being formed into films, sheets, pipes, containers, electric wires, cables, etc. by various molding methods, including extrusion and injection molding.
Since such polyolefin resins are easily flammable, various methods for making them flame-retardant have heretofore been proposed.
Of those methods, one which is adopted most commonly involves the addition of an organic flame retardant such as a halogen or phosphorus-based organic flame retardant to the polyolefin resins.
Although even a small amount of such organic flame retardant is effective, there is a drawback that a harmful gas is evolved during combustion.
Recently, in view of the above point, various methods have been studied (see Japanese Patent Laid Open Nos JP 2-53845A and 2-145632A in which hydrates of inorganometallic compounds such as aluminum hydroxide and magnesium hydroxide are used as low smoking, pollution-free type flame retardants not evolving a harmful gas during combustion.
In a flame-retardant composition using an inorganic flame retardant, it is necessary to use the inorganic flame retardant in a high ratio in order to enhance the flame retardancy of the composition. However, increasing its content makes a practical use of the composition difficult because of deterioration in mechanical strength, flexibility and processability of the composition. To remedy this drawback there also has been proposed a technique of incorporating a high concentration of a soft polyolefin resin in the composition to increase the amount of such inorganic flame retardant accepted (see U.S. Pat. Nos. 2,722,959 and 4,845,146).
However, in the case where a flame-retardant composition containing a large amount of such soft resin is used in the production of such electrically insulated materials as electric wire and cable, such electric materials as protective pipe and joint cover, such interior materials as sheet and floor material, or such molded articles as cabinet and box, the products are susceptible to external flaws caused by friction under severe conditions involving extremely high temperatures, severe vibrations during production, transport and use. Therefore, the improvement of abrasion resistance has been desired.
And to this end, there have been proposed a method of improving the abrasion resistance by crosslinking in the presence of a crosslinking aid (Japanese Patent Laid Open Nos. JP 62-252442A and 62-275139A), a method of using an ethylene/.alpha.-olefin copolymer modified with an unsaturated carboxylic acid or a derivative thereof (Japanese Patent Laid Open No. JP 2-101499A), and a method of using as a base polymer a mixture of a polyolefin resin with an ethylene resin containing carboxyl group or carboxylate in the molecule and a thermoplastic elastomer with maleic acid or maleic anhydride added in the molecule (Japanese Patent Laid Open No. JP 2-53845A). In all of these methods, however, there still remains room for improvement in point of processability and abrasion resistance, and a further improvement is desired.
It is the object of the present invention to provide an abrasion-resistant flame-retardant composition which has an improved heat resistance while retaining mechanical strength, flexibility, processability and flame retardancy and which can be used effectively in the production of molded articles, etc., including films, sheets, containers, electric wires, cables, packings, sealants, hoses and injection-molded products.